1. Field of the Invention
The present invention relates to multilayer piezoelectric components each including a plurality of internal electrodes stacked between ceramic layers. Particularly, the present invention relates to a multilayer piezoelectric actuator and a method of manufacturing the same, an ink jet head using the piezoelectric actuator, a multilayer piezoelectric resonator used as a resonator, a band pass filter, or other electronic component, and a method of manufacturing the same, a piezoelectric transformer and a method of manufacturing the same.
The present invention also relates to a piezoelectric actuator having an electrode structure which is improved so as to significantly decrease variations in displacement and a manufacturing method therefor, an ink jet head, a multilayer piezoelectric resonator including a sintered compact body having an electrode structure which is improved to significantly widen a difference xcex94F between the resonance frequency and antiresonance frequency, and to significantly decrease variations in resonance characteristics, and a manufacturing method therefor, a piezoelectric transformer having an electrode structure improved to significantly increase maximum efficiency and decrease variations in the maximum efficiency, and a manufacturing method therefor.
2. Description of the Related Art
An ink jet head of an ink jet printer uses a piezoelectric actuator for discharging a predetermined amount of ink. An example of conventional piezoelectric actuators will be described below with reference to FIG. 33.
A piezoelectric actuator 71 includes a sintered ceramic compact body 72. The sintered ceramic compact body 72 includes piezoelectric ceramic material such as lead titanate zirconate ceramic or the like.
In the sintered ceramic compact body 72, a plurality of internal electrodes 73a to 73l are arranged to overlap each other in the thickness direction. The internal electrodes 73a, 73c, 73e, 73g, 73i, and 73k are extended to the first side 72a of the sintered ceramic compact body 72. The other internal electrodes 73b, 73d, 73f, 73h, 73j, and 73l are extended to the second side 72b opposite to the first side 72a. 
First and second external electrodes 74 and 75 are disposed on the first side 72a and the second side 72b, respectively.
The ceramic layers disposed between the internal electrodes 73a to 73l are polarized in the thickness direction, as shown by arrows in FIG. 33. Namely, the ceramic layers on both sides of each of the internal electrodes are polarized in opposite directions of the thickness direction.
Therefore, application of a voltage between the external electrodes 74 and 75 causes displacement in a polarized portion of the piezoelectric actuator 71 due to a piezoelectric effect.
In an ink jet head of a conventional ink jet printer, displacement is caused in the piezoelectric actuator 71 to press an ink chamber so that a predetermined amount of ink is discharged from the ink chamber. Therefore, in order to discharge ink with high precision, it is required to decrease variations in displacement of the piezoelectric actuator 71.
However, the manufacture of many piezoelectric actuators 71 causes relatively large variations in displacement characteristics in the piezoelectric actuators. There is also the problem of causing variations in displacement in displacement portions when a plurality of notches are formed in the displacement portions of the piezoelectric actuator 71 in order to form a plurality of displacement portions.
Therefore, for example, an ink jet head of an ink jet printer including the above-described piezoelectric actuator is difficult to discharge a predetermined amount of ink with high precision.
FIG. 34 is a sectional view showing a conventional multilayer piezoelectric resonator.
A multilayer piezoelectric resonator 171 includes a sintered ceramic compact body 172 made of piezoelectric ceramic.
In the sintered ceramic compact body 172, a plurality of internal electrodes 173a to 173l are provided. The stacking direction of the internal electrodes 173a to 173l is located in the thickness direction. The sintered ceramic compact body 172 includes ceramic layers which are held between the internal electrodes in the thickness direction, and polarized as shown by arrows in FIG. 34. Namely, the adjacent ceramic layers are polarized in opposite directions in the thickness direction. The internal electrodes 173a to 173l are extended up to the opposite sides 712a and 172b of the sintered ceramic compact body 172.
Insulating films 174a to 174f and insulating films 175a to 175f are disposed on the sides 192a and 172b, respectively, of the sintered ceramic compact body 172. Each of the insulating films 174a to 174f and 175a to 175f is arranged to cover an exposed end of any one of the internal electrodes 173a to 173l on either of both sides 172a and 172b of the sintered ceramic compact body 172. Therefore, an end of each of the internal electrodes 173a to 173l is coated with any one of the insulating films 174a to 175f, the other end being exposed from the side 172a or 172b. 
External electrodes 176 and 177 are arranged to cover both sides 172a and 172b, respectively.
In the multilayer piezoelectric resonator 171, an alternating current electric field is applied between the external electrodes 176 and 177 to expand and contract the piezoelectric ceramic layers held between the respective internal electrodes 173a to 173l due to the piezoelectric effect, thereby obtaining resonance characteristics based on thickness longitudinal vibration.
However, in the piezoelectric resonator 171, resonance characteristics cannot be necessarily obtained according to design values, and a difference xcex94F between the resonance frequency and antiresonance frequency tends to be lower than the desired value. A decrease in the frequency difference xcex94F narrows the pass band of the filter.
Furthermore, the manufacture of many multilayer piezoelectric resonators 171 produces the problem of relatively large variations in resonance characteristics.
Also a Rosen-type piezoelectric transformer using a rectangular plate-shaped piezoelectric ceramic layer is conventionally known.
An example of conventional Rosen-type piezoelectric transformers will be described below with reference to FIGS. 35 and 36. A piezoelectric transformer 251 includes a rectangular plate-shaped sintered ceramic compact body 252 made of piezoelectric ceramic. The sintered ceramic compact body 252 is obtained by stacking green sheets with internal electrodes disposed therebetween, and then firing the resultant layered product, as shown in FIG. 36.
As shown in FIG. 36, green sheets 253 to 266 mainly composed of a piezoelectric ceramic powder are stacked in the direction shown in the drawing. First internal electrodes 267 are respectively disposed on the green sheets 253, 259, and 263 by screen printing conductive paste. Similarly, second internal electrodes 268 are respectively disposed on the green sheets 256, 262, and 266 by screen printing conductive paste.
Each of the first and second internal electrodes 267 and 268 contacts one end of a green sheet in the length direction. The first and second internal electrodes 267 and 268 are also arranged to overlap each other with ceramic layers held therebetween in the thickness direction. In the sintered ceramic compact body 252 (FIG. 35) as a final product, the internal electrodes 267 are exposed from the first side 252a along the longer side, and the second internal electrodes 268 are exposed from the second side 252b opposite to the first dies 252a. 
A first external electrode 269 is located in a portion of the first side 252a of the sintered ceramic compact body 252 in which the first internal electrodes 267 are exposed. Although not shown in the drawings, a second external electrode is also disposed on the second side 252b to be electrically connected to the second internal electrodes 268.
A direct-current voltage is applied between the first and second external electrodes to polarize the ceramic layers held between the respective first and second internal electrodes 267 and 268 in the thickness direction. In addition, a third external electrode 270 is disposed on a third side 252c along the short side of the sintered ceramic compact body 252.
Furthermore, a direct-current voltage is applied between the first external electrodes 269, the second external electrode and the third external electrode 270 to polarize the right-hand portion of the sintered ceramic compact body 252, where the internal electrodes 267 and 268 are not stacked, in the length direction of the sintered ceramic compact body, as shown by arrow P.
In the piezoelectric transformer 251, for example, the first external electrode 269 and the second external electrode function as input-side electrodes so that an input voltage is applied between the first and second external electrodes to excite the sintered ceramic compact body 252 in a length direction vibration mode, obtaining a stepped-up output voltage from the third external electrode 270 as an output electrode.
However, the piezoelectric transformer 251 cannot obtain maximum efficiency according to a desired value, and thus has a problem in that the maximum efficiency tends to be lower than the desired value. In addition, when the sintered ceramic compact body 252 is obtained by preparing a mother layered product for improving productivity, cutting the mother layered product into units of piezoelectric transformers 251 to obtain layered product chips, and then firing the layered product chips, or when the sintered ceramic compact body 252 is obtained by obtaining a mother sintered product, and then cutting the mother sintered product into sintered ceramic compact body 252 of piezoelectric transformer units, there is the problem of relatively large variations in maximum efficiency of the piezoelectric transformers 251 as final products.
In order to solve the above problems, preferred embodiments of the present invention provide multilayer piezoelectric components which minimize variations in component characteristics.
Preferred embodiments of the present invention provide a piezoelectric actuator causing less variation in displacement and a manufacturing method therefor, and an ink jet head capable of discharging a predetermined ink with high precision by using the actuator.
Preferred embodiments of the present invention also provide a multilayer piezoelectric resonator exhibiting a large difference xcex94F between the resonance frequency and antiresonance frequency, and excellent resonance characteristics and minimizing variation in resonance characteristics, and a manufacturing method therefor.
Preferred embodiments of the present invention further provide a piezoelectric transformer which achieves an increase in maximum efficiency, and an effective decrease in variations in maximum efficiency.
As a result of study of the reason why large variations in displacement are caused in the piezoelectric actuator 71, it was confirmed that a constituent metal of the internal electrodes 73a to 73l in the sintered ceramic compact body 72 diffuses during firing to produce dimensions which deviate from design values, thereby causing variations in displacement. Therefore, it was discovered that a piezoelectric actuator causing significantly less variation in displacement can be obtained by suppressing diffusion of a constituent metal of the internal electrodes during firing. This led to the achievement of preferred embodiments of the present invention.
In other words, a piezoelectric actuator according to preferred embodiments of the present invention has a structure in which diffusion of a constituent metal of internal electrodes is suppressed during firing, thereby decreasing variations in displacement.
As a result of study of the reason why a conventional multilayer piezoelectric resonator causes a small frequency difference xcex94F and variations in resonance characteristics, the inventors also discovered that a metal used in internal electrodes, for example, silver, diffuses into ceramic during firing which causes the internal electrodes to be different from to design values. Therefore, the inventors considered that by suppressing the diffusion of the internal electrode constituent metal into ceramic, the frequency difference xcex94F can be greatly increased, and variations in resonance characteristics can be minimized. This led to the achievement of preferred embodiments of the present invention.
Furthermore, as a result of various studies in consideration of the phenomenon that a maximum efficiency according to design values cannot be obtained in the conventional piezoelectric transformer 251, the inventors discovered that in the sintered ceramic compact body 252 as a final product, the internal electrodes 267 and 268 having dimensions according to design values cannot be obtained, and electrodes are partially broken. A constituent metal of the internal electrodes, such as silver, which constitutes the internal electrodes, diffuses to the ceramic side during firing to prevent formation of the internal electrodes according to design values, thereby decreasing the maximum efficiency and causing variations in the maximum efficiency.
In other words, on the basis of the above-mentioned findings and discoveries, the inventors determined that by suppressing diffusion of a constituent metal of the internal electrodes during ceramic firing, the maximum efficiency can be greatly improved, and variations in the maximum efficiency can be minimized. This led to the achievement of preferred embodiments of the present invention.
Preferred embodiments of the present invention further provide a multilayer piezoelectric component including a sintered ceramic compact body made of piezoelectric ceramic and having opposite first and second sides, first and second external electrodes respectively disposed on the first and second sides of the sintered ceramic compact body, a plurality of internal electrodes stacked in the sintered ceramic compact body to overlap each other with ceramic layers held therebetween in the thickness direction, the internal electrodes being arranged to be electrically connected to the first or second external electrode; and a dummy electrode located at a height where at least one of the internal electrodes is provided, between an end of the at least one internal electrode opposite to the end connected to one of the external electrodes, and the other external electrode to which the at least one internal electrode is not connected.
The unique arrangement of the dummy electrode suppresses diffusion of the constituent metal of the internal electrodes toward the dummy electrode from the internal electrodes.
Preferred embodiments of the present invention further provides a piezoelectric actuator having the above-described construction.
In the piezoelectric actuator, in addition to the dummy electrode, a floating electrode may be provided to suppress the diffusion of the constituent metal of the internal electrodes in the thickness direction. In this case, as the floating electrode, at least one layer is preferably disposed in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction and/or the ceramic layers outside the outermost internal electrodes in the stacking direction.
In the piezoelectric actuator, the distance between the dummy electrode-side end of one of the internal electrodes and the dummy electrode is preferably about 100 xcexcm or less, thereby effectively suppressing the diffusion of the internal electrode constituent metal to the dummy electrode side. With this distance over 100 xcexcm, there is the small effect of suppressing the diffusion of the internal electrode constituent metal by providing the dummy electrode.
Preferred embodiments of the present invention further provide a multilayer piezoelectric resonator having the above construction.
A preferred embodiment of the present invention provides a multilayer piezoelectric component, which constitutes a piezoelectric transformer including the sintered ceramic compact body made of piezoelectric ceramic and having a substantially rectangular plate shape having the opposite first and second sides located on the longer side thereof, and opposite third and fourth sides located on the shorter side, the first and second external electrodes respectively located on portions of the first and second sides of the sintered ceramic compact body, which are close to the fourth side thereof, a third external electrode provided on the third side of the sintered ceramic compact body; the plurality of internal electrodes stacked in the sintered ceramic compact body to overlap each other with ceramic layers held therebetween in the thickness direction, and to be electrically connected to the first or second external electrode and the dummy electrode provided at the height where at least one of the internal electrodes is located, between the end of the at least one internal electrode opposite to the end connected to one of the external electrodes, and the other external electrode to which the at least one internal electrode is not connected.
The multilayer piezoelectric component may further include at least one floating electrode layer disposed in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction of the internal electrodes and/or the ceramic layers outside the outermost internal electrodes in the stacking direction, and arranged so as not to be electrically connected to the first and second external electrodes.
In the multilayer piezoelectric component, the distance between the dummy electrode-side end of one of the internal electrodes and the dummy electrode is preferably in the range from the thickness of each of the ceramic layers between the internal electrodes to about 300 xcexcm.
Preferred embodiments of the present invention further provide a multilayer piezoelectric component including a sintered ceramic compact body made of piezoelectric ceramic and having opposite first and second sides, first and second external electrodes respectively disposed on the first and second sides of the sintered ceramic compact body, a plurality of internal electrodes stacked in the sintered ceramic compact body to overlap each other with ceramic layers held therebetween in the thickness direction, and to be electrically connected to the first or second external electrode, and at least one floating electrode layer disposed in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction of the internal electrodes and/or the ceramic layers outside the outermost internal electrodes in the stacking direction, and arranged so as not to be electrically connected to the first and second external electrodes.
The multilayer piezoelectric component may constitute a piezoelectric actuator or a multilayer piezoelectric resonator.
When the multilayer piezoelectric component constitutes a multilayer piezoelectric resonator, the internal electrodes and the floating electrode are arranged to extend up to the first and second sides of the sintered ceramic compact body, and insulating films may be further provided to cover exposed portions of the internal electrodes and/or the floating electrode on the first and second sides of the sintered ceramic compact body so that the internal electrodes are electrically connected to the first or second external electrode but not electrically connected to the other external electrode, and the floating electrode is not electrically connected to the external electrodes.
When the multilayer piezoelectric component constitutes a multilayer piezoelectric resonator, at least one dummy electrode may be provided between the end of at least one of the internal electrodes opposite to the end electrically connected to one of the external electrodes, and the other external electrode to which the internal electrode is not connected, in a plane where the at least one internal electrode is provided.
When the multilayer piezoelectric component constitutes a multilayer piezoelectric resonator, a plurality of floating electrode layers may be arranged in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction of the internal electrodes and/or the ceramic layers outside the outermost internal electrodes in the stacking direction.
Preferred embodiments of the present invention further provide the multilayer piezoelectric component which constitutes a piezoelectric transformer including the sintered ceramic compact body made of piezoelectric ceramic and having a substantially rectangular plate shape having the opposite first and second sides located on the longer side thereof, and opposite third and fourth sides located on the shorter side thereof, the first and second external electrodes respectively disposed on portions of the first and second sides of the sintered ceramic compact body, which are close to the fourth side thereof, the plurality of internal electrodes stacked in the sintered ceramic compact body to overlap each other with ceramic layers disposed therebetween in the thickness direction, and to be electrically connected to the first or second external electrode, and the at least one floating electrode layer disposed in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction of the internal electrodes and/or the ceramic layers outside the outermost internal electrodes in the stacking direction, and arranged so as not to be electrically connected to the first and second external electrodes.
Preferred embodiments of the present invention further provide a method of manufacturing a piezoelectric actuator including the steps of printing an internal electrode and dummy electrode on a green sheet including piezoelectric ceramic material, stacking a plurality of the green sheets, each having the internal electrode and the dummy electrode printed thereon, to obtain a layered product in which the plurality of internal electrodes extend to first and second sides alternately in the stacking direction, and the dummy electrodes are respectively arranged between the ends of the internal electrodes opposite to the ends extended to the first or second side, and the side to which the internal electrodes are not extended, firing the layered product to obtain a sintered ceramic compact body, respectively forming first and second external electrodes on the first and second sides of the sintered ceramic compact body, and applying a DC electric field between the first and second external electrodes to polarize the sintered ceramic compact body.
Preferred embodiments of the present invention further provide a method of manufacturing a piezoelectric actuator including the steps of printing an internal electrode and dummy electrode on a green sheet including piezoelectric ceramic material, printing a floating electrode on a green sheet, stacking a plurality of green sheets, each having an internal electrode and a dummy electrode printed thereon, and the green sheet on which the floating electrode is printed, to obtain a layered product in which at least one floating electrode is arranged in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction and/or the ceramic layers outside the outermost internal electrodes in the stacking direction, the plurality of internal electrodes being extended to first and second sides alternately in the stacking direction, and the dummy electrodes are respectively arranged between the ends of the internal electrodes opposite to the ends led to the first or second side, and the side to which the internal electrodes are not extended, firing the layered product to obtain a sintered ceramic compact body, respectively forming first and second external electrodes on the first and second sides of the sintered ceramic compact body, and applying a DC electric field between the first and second external electrodes to polarize the sintered ceramic compact body.
Preferred embodiments of the present invention further provide a method of manufacturing a multilayer piezoelectric resonator including the steps of printing an internal electrode pattern on a green sheet to obtain a first green sheet, printing a floating electrode pattern on a green sheet to obtain a second green sheet, stacking the first and second green sheets so that the floating electrode pattern is arranged on at least one of the green sheets between the adjacent internal electrode patterns in the stacking direction and/or the green sheets outside the outermost internal electrode patterns in the stacking direction to obtain a layered product, firing the layered product to obtain a mother sintered ceramic compact body, polarizing the mother sintered ceramic compact body by using the internal electrode patterns of the mother sintered ceramic compact body, cutting the mother sintered ceramic compact body to obtain a sintered ceramic compact body of a piezoelectric resonator unit, and respectively forming first and second external electrodes on opposite first and second sides of the sintered ceramic compact body so that the internal electrodes are electrically connected to only one of the external electrodes, and the floating electrode is not electrically connected to the external electrodes.
Preferred embodiments of the present invention provide a method of manufacturing a multilayer piezoelectric resonator wherein internal electrodes and a floating electrode are formed to extend up to first and second sides of the sintered ceramic compact body of each multilayer piezoelectric resonator unit, and the step of forming external electrodes on the first and second sides of the sintered ceramic compact body includes the steps of forming insulating films on the first and second sides of the sintered ceramic compact body to cover exposed portions of the internal electrodes and/or the floating electrode so that the internal electrodes are electrically connected to only one of first and second external electrodes but not electrically connected to the other external electrode, and the floating electrode is not electrically connected to the external electrodes, and forming the first and second external electrodes on the first and second sides of the sintered ceramic compact body after forming the insulating films.
In the method of manufacturing a multilayer piezoelectric resonator according to this preferred embodiment, in the step of obtaining the first green sheet, the internal electrode pattern and dummy electrode pattern may be printed on the green sheet.
In the method of manufacturing a multilayer piezoelectric resonator according to another preferred embodiment, in the step of obtaining the second green sheet, the floating electrode pattern and dummy electrode pattern may be printed on the green sheet.
Preferred embodiments of the present invention further provide a method of manufacturing a multilayer piezoelectric resonator including the steps of printing an internal electrode pattern and dummy electrode pattern on a green sheet to obtain a first green sheet, stacking at least a plurality of the first green sheets to obtain a mother layered product, firing the mother layered product to obtain a mother sintered ceramic compact body, polarizing the mother sintered ceramic compact body by using the internal electrode patterns, cutting the mother sintered ceramic compact body to obtain a sintered ceramic compact body of each piezoelectric resonator unit and respectively forming first and second external electrodes on opposite first and second sides of the sintered ceramic compact body so that the internal electrodes are electrically connected to at least one of the external electrodes.
Preferred embodiments of the present invention further provide a method of manufacturing a piezoelectric transformer including the steps of printing an internal electrode and dummy electrode on a green sheet, stacking a plurality of the green sheets each having the internal electrode and the dummy electrode printed thereon, to obtain a layered product having opposite third and fourth sides, in which the plurality of internal electrodes are extended to the opposite first and second sides alternately in the thickness direction, and the dummy electrodes are respectively arranged between the ends of the internal electrodes opposite to the ends extended to one of the external sides, and the other side to which the internal electrodes are not extended, firing the layered product to obtain a sintered ceramic compact body, respectively forming first and second external electrodes on portions of the first and second sides of the sintered ceramic compact body, to which the internal electrodes are extended, so that the external electrodes close to the fourth side, forming a third external electrode on the third side of the sintered ceramic compact body, and applying a DC electric field between the first and second external electrodes and the third external electrode to polarize the sintered ceramic compact body.
Preferred embodiments of the present invention further provide a method of manufacturing a piezoelectric transformer including the steps of printing an internal electrode and dummy electrode on a green sheet, printing a floating electrode on a green sheet, stacking a plurality of the green sheets each having the internal electrode and the dummy electrode printed thereon, and the green sheet on which the floating electrode is printed, to obtain a layered product having opposite third and fourth sides, in which at least one floating electrode layer is arranged in at least one of the ceramic layers between the adjacent internal electrodes in the stacking direction and/or the ceramic layers outside the outermost internal electrodes in the stacking direction, the plurality of internal electrodes are extended to the opposite first and second sides alternately in the thickness direction, and the dummy electrodes are respectively arranged between the ends of the internal electrodes opposite to the ends extended to one of the first and second sides, and the other side to which the internal electrodes are not extended, firing the layered product to obtain a sintered ceramic compact body, respectively forming first and second external electrodes on portions of the first and second sides of the sintered ceramic compact body, to which the internal electrodes are extended, so that the external electrodes are close to the fourth side, forming a third external electrode on the third side of the sintered ceramic compact body, and applying a DC electric field between the first and second external electrodes to polarize the sintered ceramic compact body, and applying a DC electric field between the first and second external electrodes and the third external electrode to polarize the sintered ceramic compact body.
Preferred embodiments of the present invention further provide an ink jet head including a nozzle for discharging ink, an ink chamber communicated with the nozzle and including at least one flexible wall, and any one of the above-described piezoelectric actuators arranged near the ink chamber, for pressing the ink chamber.
Other features, elements, applications, uses and advantages of the present invention will become apparent from the detailed description of preferred embodiments of the present invention below with reference to the attached drawings.